/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }Math.min(l1.val,l2.val) ? l1:l2;
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null) {
            return l2;
        }
        if(l2 == null) {
            return l1;
        }
        ListNode cur =  new ListNode(-1);
        ListNode curr = cur;
        while(l1 != null && l2 != null) {
            if(l1.val < l2.val) {
                cur.next = l1;
                cur = cur.next;
                l1 = l1.next;
            } else {
                cur.next = l2;
                cur = cur.next;
                l2 = l2.next;
            }
        }
        while(l1 != null) {
            cur.next = l1;
            cur = cur.next;
            l1 = l1.next;
        }
        while(l2 != null) {
            cur.next = l2;
            cur = cur.next;
            l2 = l2.next;
        }
        return curr.next;
    }
}